Cytotoxic T lymphocytes (CTL) offer a unique group of therapeutic effectors to dissect and amplify mechanisms of host-resistance to autologous tumor and define tumor Ag by therapeutic T cells (TIL). During the previous phase of our research peptides corresponding to locations on C-erb-B-2 gene product (pHER2/neu) comprising T cell epitope motifs were demonstrated to render resistant targets, sensitive to lysis by tumor specific CTL isolated from ovarian TIL, which are currently under study as potential therapeutic effectors. The studies proposed herein represent extensions to nominal peptide Ag of our previous studies (1,2) and aim to understand the mechanisms of recognition and action of potentially immunotherapeutic T cells in the ovarian tumor model with future extension to breast cancer. Specifically, we will: 1. Map CTL epitopes on pHER2 potential T cell sites with synthetic peptides. We will determine: (a) the fine specificity of CTL-TIL clones: (b) define the boundaries of T cell epitopes by identifying residues critical for TCR recognition and CTL function. 2. Determine whether epitopes mapped with synthetic peptides correspond to epitopes on HER2 protein. 3. Ascertain whether CD4 cells from TIL and PBMC of ovarian patients recognize pHER2 epitopes. We will determine whether: (a) CD4 cells respond to recombinant pHER2 in the context of MHC class II, and these responses can be located with the same synthetic peptides corresponding to potential T cell sites. This may help define immunodominant epitopes and determine whether, as expected, pHER2 is a tumor Ag recognized by CTL-TIL. The proposed studies, may define mechanisms of tumor recognition by T cells and provide a modus operandi for elimination of oncogene driven tumor cells by immunotherapy.